Circadian Aspects of Postprandial Metabolism

Time‐dependent variations in the hormonal and metabolic responses to food are of importance to human health, as postprandial metabolic responses have been implicated as risk factors in a number of major diseases, including cardiovascular disease. Early work reported decreasing glucose tolerance in the evening and at night with evidence for insulin resistance at night. Subsequently an endogenous circadian component, assessed in constant routine (CR), as well as an influence of sleep time, was described for glucose and insulin. Plasma triacylglycerol (TAG), the major lipid component of dietary fat circulating after a meal, also appears to be influenced by both the circadian clock and sleep time with higher levels during biological night (defined as the time between the onset and offset of melatonin secretion) despite identical hourly nutrient intake. These time‐dependent differences in postprandial responses have implications for shiftworkers. In the case of an unadapted night shift worker, meals during work time will be taken during biological night. In simulated night shift conditions the TAG response to a standard meal, preceded by either a low‐fat or a high‐fat premeal, was higher after a nighttime meal than during a daytime meal, and the day/night difference was larger in men than in women. In real night shift workers in Antarctica, insulin, glucose, and TAG all showed an increased response after a nighttime meal (second day of night shift) compared to a daytime meal. Night shift workers are reported to have an approximately 1.5 times higher incidence of heart disease risk and also demonstrate higher TAG levels compared with matched dayworkers. As both insulin resistance and elevated circulating TAG are independent risk factors for heart disease, it is possible that meals at night may contribute to this risk.     

Circadian Variation in Alloxan Sensitivity of Mice as Indicated by Mortality and Blood Glucose Alteration

The objective of this study was to determine in mice if a time-dependent pancreatic β-cell susceptibility to alloxan could be correlated to daily changes in blood glucose levels and to monitor the pattern of blood glucose at various times of day as mice became diabetic. Food was removed from mice standardized to a 12-h light:dark cycle (lights on at 0600 h CST, during the month of June) at 12 h before subcutaneous injection with 0.27 mg/g of alloxan. Six groups of 30 fasted mice were injected at 4-h intervals. Blood glucose levels were measured from each group immediately prior to injection, and at 2, 4, 8, 12, 24, 48, and 216 h after treatment. Animals receiving alloxan during the early- to middark period had an increase in blood glucose after 2 h, followed by a decline to hypoglycemic levels between 4 and 8 h, and recovery to hyperglycemic levels 48 h after alloxan exposure. Three and 30% of these animals were dead at 8 and 48 h, respectively. Mice treated during the midlight span had decreased blood glucose levels 2 h after alloxan treatment followed by an increase to diabetic hyperglycemia within 48 h. Twenty-three and 70% of the animals treated at 1430 h were dead at 8 and 48 h, respectively. At 216 h, total mortality was 45.6% and 81 of the 98 surviving mice were hyperglycemic. These data suggest a greater sensitivity to alloxan during the midlight resting period of the mice. This may be the result of increased sensitivity to the insulin released from the β cells when alloxan was given during the light span.     

在基因家族背景下对四种植物中DGAT2的鉴定和序列分析

二酰甘油酰基转移酶2(Diacylglycerol O-acyltransferase 2,DGAT2)是植物中三羧酸甘油酯(TAG)合成途径的限速酶,其编码基因属于酰基转移酶基因超家族。本研究依托植物全基因组数据库Phytozome,通过BLAST搜索获得了蓖麻(Ricinus communis L.)、拟南芥(Arabidopsis thaliana Heynh.)、毛果杨(Populus tricho-carpa Torr.A.Gray.)和木薯(Manihot esculenta Crantz.)4种双子叶植物酰基转移酶基因超家族所编码的73条多肽序列,并从中鉴定出5条DGAT2序列。理化性质和跨膜结构域分析表明,5条DGAT2序列均为疏水性跨膜蛋白,其中木薯DGAT2为一次跨膜蛋白且在叶绿体膜中大量分布,这与其他植物的DGAT2序列存在差异;木薯DGAT2蛋白在进化过程中发生了功能分化且可能与木薯的抗逆作用有关。     

Circadian changes of heart rate in West syndrome

Patterns of circadian and ultradian rhythms in the heart rate (HR) are described in a full-term baby with birth asphyxia and convulsions. A 24h HR recording was carried out at the age of 1, 15, 56, 289, and 295 days; West syndrome diagnosis was made when the patient was 3 months old. The HR showed no circadian rhythm in the follow-up, whereas it is known that the circadian rhythm appears in healthy infants at the age of 1 month and remains thereafter. This observation may be an indirect indicator of the interference of West syndrome with centers of neurological maturity. (Chronobiology International, 17(4), 591-595, 2000)     

Pathway-selective Insulin Resistance and Metabolic Disease: The Importance of Nutrient Flux

Hepatic glucose and lipid metabolism are altered in metabolic disease (e.g. obesity, metabolic syndrome, and Type 2 diabetes). Insulin-dependent regulation of glucose metabolism is impaired. In contrast, lipogenesis, hypertriglyceridemia, and hepatic steatosis are increased. Because insulin promotes lipogenesis and liver fat accumulation, to explain the elevation in plasma and tissue lipids, investigators have suggested the presence of pathway-selective insulin resistance. In this model, insulin signaling to glucose metabolism is impaired, but insulin signaling to lipid metabolism is intact. We discuss the evidence for the differential regulation of hepatic lipid and glucose metabolism. We suggest that the primary phenotypic driver is altered substrate delivery to the liver, as well as the repartitioning of hepatic nutrient handling. Specific alterations in insulin signaling serve to amplify the alterations in hepatic substrate metabolism. Thus, hyperinsulinemia and its resultant increased signaling may facilitate lipogenesis, but are not the major drivers of the phenotype of pathway-selective insulin resistance.     

三角褐指藻甘油酯对氮胁迫的响应

【背景】三角褐指藻作为生物燃料潜在的生产者,在胁迫条件下能通过改变其甘油酯组成来适应外部环境的变化,同时伴随着生物燃料原料甘油三酯(TAG)的积累,研究三角褐指藻甘油酯对氮胁迫的响应机制有利于深入认识TAG的积累过程。【目的】通过分析三角褐指藻在正常和氮胁迫条件下各类脂质含量及其脂肪酸成分的变化,揭示氮胁迫诱导积累的TAG酰基主要来源,以及在胁迫前生成的各极性甘油酯脂肪酸的去向,从而为进一步认识三角褐指藻对氮胁迫的响应机制提供新信息。【方法】利用高效薄层色谱结合气相色谱法分析三角褐指藻在正常和氮胁迫条件下的脂肪酸及甘油酯组分的变化。【结果】三角褐指藻在氮胁迫条件下TAG含量增加至57.8 mg/g时,总甘油酯含量几乎不变,但各甘油酯含量变化差异很大,表现为各极性脂含量显著降低。在此期间,各类甘油酯脂肪酸组成含量的变化表明,三角褐指藻TAG主要积累饱和及单不饱和脂肪酸,即16:0和16:1n7,分别以从头合成及原有极性脂转化为主,极性脂的部分二十碳五烯酸(EPA)作为酰基供体也向TAG发生了转化;此外组成极性脂的多不饱和脂肪酸16:2n4、16:3n4及EPA分解导致其含量显著下降。【结论】当氮胁迫诱导的三角褐指藻TAG含量为57.8 mg/g时,积累的TAG酰基中有48%来自从头合成,52%来自极性脂转化;而氮胁迫诱导所减少的极性脂酰基中有54%转化成TAG,46%发生了分解。     

Postprandial Metabolic Profiles Following Meals and Snacks Eaten during Simulated Night and Day Shift Work

Shift workers are known to have an increased risk of developing cardiovascular disease (CVD) compared with day workers. An important factor contributing to this increased risk could be the increased incidence of postprandial metabolic risk factors for CVD among shift workers, as a consequence of the maladaptation of endogenous circadian rhythms to abrupt changes in shift times. We have previously shown that both simulated and real shift workers showed relatively impaired glucose and lipid tolerance if a single test meal was consumed between 00:00–02:00 h (night shift) compared with 12:00–14:00 h (day shift). The objective of the present study was to extend these observations to compare the cumulative metabolic effect of consecutive snacks/meals, as might normally be consumed throughout a period of night or day shift work. In a randomized crossover study, eight healthy nonobese men (20–33 yrs, BMI 20–25 kg/m²) consumed a combination of two meals and a snack on two occasions following a standardized prestudy meal, simulating night and day shift working (total energy 2500 kcal: 40% fat, 50% carbohydrate, 10% protein). Meals were consumed at 01:00/13:00 h and 07:00/19:00 h, and the snack at 04:00/16:00 h. Blood was taken after an overnight fast, and for 8 h following the first meal on each occasion, for the measurement of glucose, insulin, triacylglycerol (TAG), and nonesterified fatty acids (NEFA). RM-ANOVA (factors time and shift) showed a significant effect of shift for plasma TAG, with higher levels on simulated night compared to day shift (p < 0.05). There was a trend toward an effect of shift for plasma glucose, with higher plasma glucose at night (p = 0.08), and there was a time-shift interaction for plasma insulin levels (p < 0.01). NEFA levels were unaffected by shift. Inspection of the area under the plasma response curve (AUC) following each meal and snack revealed that the differences in lipid tolerance occurred throughout the study, with greatest differences occurring following the mid-shift snack. In contrast, glucose tolerance was relatively impaired following the first night-time meal, with no differences observed following the second meal. Plasma insulin levels were significantly lower following the first meal (p < 0.05), but significantly higher following the second meal (p < 0.01) on the simulated night shift. These findings confirm our previous observations of raised postprandial TAG and glucose at night, and show that sequential meal ingestion has a more pronounced effect on subsequent lipid than carbohydrate tolerance.     

Influence of the hepatic eukaryotic initiation factor 2alpha (eIF2alpha) endoplasmic reticulum (ER) stress response pathway on insulin-mediated ER stress and hepatic and peripheral glucose metabolism

Recent studies have implicated endoplasmic reticulum (ER) stress in insulin resistance associated with caloric excess. In mice placed on a 3-day high fat diet, we find augmented eIF2α signaling, together with hepatic lipid accumulation and insulin resistance. To clarify the role of the liver ER stress-dependent phospho-eIF2α (eIF2α-P) pathway in response to acute caloric excess on liver and muscle glucose and lipid metabolism, we studied transgenic mice in which the hepatic ER stress-dependent eIF2α-P pathway was inhibited by overexpressing a constitutively active C-terminal fragment of GADD34/PPP1R15a, a regulatory subunit of phosphatase that terminates ER stress signaling by phospho-eIF2α. Inhibition of the eIF2α-P signaling in liver led to a decrease in hepatic glucose production in the basal and clamped state, which could be attributed to reduced gluconeogenic gene expression, resulting in reduced basal plasma glucose concentrations. Surprisingly, hepatic eIF2α inhibition also impaired insulin-stimulated muscle and adipose tissue insulin sensitivity. This latter effect could be attributed at least in part by an increase in circulating IGFBP-3 levels in the transgenic animals. In addition, infusion of insulin during a hyperinsulinemic-euglycemic clamp induced conspicuous ER stress in the 3-day high fat diet-fed mice, which was aggravated through continuous dephosphorylation of eIF2α. Together, these data imply that the hepatic ER stress eIF2α signaling pathway affects hepatic glucose production without altering hepatic insulin sensitivity. Moreover, hepatic ER stress-dependent eIF2α-P signaling is implicated in an unanticipated cross-talk between the liver and peripheral organs to influence insulin sensitivity, probably via IGFBP-3. Finally, eIF2α is crucial for proper resolution of insulin-induced ER stress.     

Circadian Rhythm of Blood Pressure and Heart Rate in Cardiopathic Patients Before and After Heart Transplantation

The aim of this study was to investigate the natural history of the circadian rhythm of blood pressure (BP) and heart rate (HR) in 10 patients with heart failure (class IV of the New York Heart Association), who underwent heart transplantation because of primary congestive cardiomyopathy. The control group was 10 age-matched clinically healthy subjects. The BP and HR monitor-ings were performed before and after transplantation. Preoperatively, analysis of variance and cosinor methods validated the occurrence of a statistically significant BP and HR circadian rhythm in cardiopathic patients. Over the 4 days after surgery, both the cosinor method and serial section analysis were unable to validate a 24-h periodicity for BP and HR in patients with heart transplants. Six months after surgery, the BP and HR circadian rhythm was not detected as well. One year after transplantation. the BP and HR circadian rhythm was statistically validated. The recovery of the BP and HR circadian rhythm 1 year after heart transplantation can be regarded as a clinical sign of a reacquired susceptibility to neurovegetative chronoregulation.     

Short-term administration of C. aronia stimulates insulin signaling,suppresses fatty acids metabolism,and increases glucose uptake and utilization in the hearts of healthy rats

This study evaluated the effect of Crataegus aronia (C. aronia) aqueous extract on cardiac substrate utilization and insulin signaling in adult male healthy Wistar rats. Rats (n = 18/group) were either administered normal saline (vehicle) or treated with C. aronia aqueous extract (200 mg/kg) for 7 days, daily. Fasting plasma glucose and insulin levels were not significantly changed in C. aronia-treated rats but were significantly reduced after both the intraperitoneal glucose or insulin tolerance tests. Besides, C. aronia significantly increased the left ventricular (LV) activities of phosphofructokinase (PFK) and pyruvate dehydrogenase (PDH), two markers of glycolysis and glucose oxidation, respectively, and suppressed the levels of pyruvate dehydrogenase kinase 4 (PDK4), an inhibitor of PDH. Concomitantly, it significantly reduced the LV levels of carnitine palmitoyltransferase 1 (CPT1) and PPARα, two markers of fatty acid (FAs) oxidations. Under basal and insulin stimulation, C. aronia aqueous extract boosted insulin signaling in the LV of rats by increasing the protein levels of p-IRS (Tyr⁶¹²) and p-Akt (Ser⁴⁷³) and suppressing protein levels of p-mTOR (Ser 2448) and p-IRS (Ser³⁰⁷). In parallel, C. aronia also increased the protein levels of GLUT-4 in the membrane fraction of the treated LVs. All these effects were also associated with a significant increase in AMPK activity (phosphorylation at Thr¹⁷²), a major energy modulator that stimulates glucose utilization. In conclusion, short-term administration of C. aronia aqueous extract shifts the cardiac metabolism toward glucose utilization, thus making this plant a potential therapeutic medication in cardiac disorders with impaired metabolism.     

Cerebral Cortical Glucose Utilization in the Conscious Rat: Evidence for a Circadian Rhythm

Abstract: The presence of a circadian rhythm of glucose utilization was demonstrated in vivo in rat cerebral cortex. The activity pattern of the rats, living in a controlled lighting regimen with lights on from 7 a.m. to 7 p. m., appeared to coincide with the rate of glucose consumption in the brain. The rate of utilization was measured at 3-h intervals throughout the day and was found to fall from a maximum at 3 a.m. of 0.98 ± 0.13 μmol min⁻¹ g⁻¹ to a minimum of 0.70 ± 0.08 μmol min⁻¹ g⁻¹ at 3 p. m. Brain glucose also varied with time and its fluctuating level weakly correlated with its rate of utilization. Animals entrained on a 5-h (4: 30-9: 30 p. m.) feeding schedule had a similar circadian rhythm, with only a slight increase in amplitude. Reversal of the light cycle caused a disruption in the normal rhythm, but utilization still varied significantly with time of day. The results both indicate the potential error that can be encountered in experiments done at different times of the day and stress the need for awareness of time of day as a factor in measurements of alterations of metabolic rate in the brain.     

Molecular modeling,docking and dynamics analysis of lipid droplet associated enzyme Ypr147cp from Saccharomyces cerevisiae

Ypr147cp of Saccharomyces cerevisiae was localized to lipid droplets. The recombinant Ypr147cp showed both triacylglycerol lipase and ester hydrolase activities. Knock out of YPR147C led to accumulation of TAG in ypr147cΔ when compared to wild type (WT). Transmission electron microscopic analysis of ypr147cΔ cells show increased lipid bodies. Moreover, the lipid profiling confirmed the accumulation of fatty acids derived from neutral and phospholipids in ypr147cΔ cells. Sequence analysis of Ypr147cp show the presence of an a/b hydrolase domain with the conserved GXSXG lipase motif. The YPR147c homology model was built and the modeled protein was analysed using RMSD and root mean square fluctuation (RMSF) for a 100 ns simulation trajectory. Docking the acetate, butyrate and palmitate ligands with the model confirmed covalent binding of ligands with the Ser207 of the GXSXG motif. Thus, Ypr147cp is a lipid droplet associated triacylglycerol lipase having short chain ester hydrolyzing capacity.     

Insulin down-regulates cardioprotective SUR2A in the heart-derived H9c2 cells: A possible explanation for some adverse effects of insulin therapy

Some recent studies associated insulin therapy with negative cardiovascular events and shorter lifespan. SUR2A, a K_ATP channel subunit, regulate cardioprotection and cardiac ageing. Here, we have tested whether glucose and insulin regulate expression of SUR2A/K_ATP channel subunits and resistance to metabolic stress in heart H9c2 cells. Absence of glucose in culture media decreased SUR2A mRNA, while mRNAs of Kir6.2, Kir6.1, SUR1 and IES SUR2B were increased. 2-deoxyglucose (50 mM) decreased mRNAs of SUR2A, SUR2B and SUR1, did not affect IES SUR2A and IES SUR2B mRNAs and increased Kir6.2 mRNA. No glucose and 2-deoxyglucose (50 mM) decreased resistance to an inhibitor of oxidative phosphorylation, DNP (10 mM). 50 mM glucose did not alter K_ATP channel subunits nor cellular resistance to DNP (10 mM). Insulin (20 ng/ml) in both physiological and high glucose (50 mM) down-regulated SUR2A while upregulating Kir6.1 and Kir6.2 (in high glucose only). Insulin (20 ng/ml) in physiological and high glucose decreased cell survival in DNP (10 mM). As opposed to Kir6.2, infection with SUR2A resulted in titre-dependent cytoprotection. We conclude that insulin decreases resistance to metabolic stress in H9c2 cells by decreasing SUR2A expression. Lower cardiac SUR2A levels underlie increased myocardial susceptibility to metabolic stress and shorter lifespan.     

Bone and glucose metabolism: A two-way street

Evidence from rodent models indicates that undercarboxylated osteocalcin (ucOC), a product of osteoblasts, is a hormone affecting insulin production by the pancreas and insulin sensitivity in peripheral tissues, at least in part through enhanced secretion of adiponectin from adipocytes. Clinical research to test whether this relationship is found in humans is just beginning to emerge. Cross-sectional studies confirm associations between total osteocalcin (OC), ucOC and glucose metabolism but cannot distinguish causality. To date, longitudinal studies have not provided a consistent picture of the effects of ucOC or OC on fasting glucose and insulin sensitivity. Further exploration into the physiological and mechanistic effects of ucOC and OC, in rodent models and clinical studies, is necessary to determine to what extent the skeleton regulates energy metabolism in humans.     

环境光导致昼夜节律紊乱对睡眠的影响

目的:研究通过环境光扰乱正常昼夜节律对睡眠的影响。方法:使用小鼠昼夜节律模型(20小时一个循环,10小时见光,10小时避光),利用小鼠睡眠生物解析系统,记录脑电波和肌电波,分析睡眠觉醒量、不同时间睡眠觉醒波delta功率和睡眠时相转换等参数。结果:昼夜节律干扰后导致昼夜觉醒差异、非快速眼动睡眠差异(NREM),和快速眼动睡眠(REM)差异消失(P0.05),昼夜节律干扰后增加了觉醒和NREM睡眠之间的转换次数(P0.05),昼夜节律紊乱的光照时相在开始时没有delta功率减弱征象(P0.05)。结论:昼夜节律模型不会导致典型的睡眠剥夺,但是会对睡眠时间和质量会产生影响。本研究一步证实昼夜节律对睡眠调节有着重要的作用。     

Circadian rhythm in the number of granulated vesicles in the pinealocytes of mice

Summary Adult, Charles River CD-1, male mice were housed in an environmental control chamber under strict conditions of controlled light (12D/12L) and temperature. The mice were sacrificed at various times throughout the twenty-four hour clock and their pineals prepared routinely for electron microscopy. The number of dense-cored or granulated vesicles present in the polar terminals of pinealocytes were quantitated in thin cross sections through pericapillary areas. A distinct circadian rhythm was observed in the number of granulated vesicles with a three- to four-fold difference between late photoperiod maximum and late dark period minimum. The rhythm was abolished by bilateral superior cervical ganglionectomy. These results are consistent with the hypothesis that the granulated vesicles are synthesized and stored in the pinealocytic cytoplasm during the photoperiod under the tropic influence of norepinephrine, and are released during the dark period when melatonin synthesis is greatest. Melatonin, administered as daily intraperitoneal doses of 50 g over a period of five days, was observed to increase markedly the number of pinealocytic granulated vesicles during the light period, but led during the dark period to a decrease in their numbers to levels below that of diluent-treated controls. It may be that melatonin stimulates the synthesis and/or release of granulated vesicles which represent the packaged form of a major secretory product.Supported in part by N.I.H. Grant No. HD 08795     

昼夜节律紊乱与胰岛β细胞缺陷关系的研究进展

生物的许多生命现象多有其固有的周期,呈现出昼夜节律、月节律和年节律性。昼夜节律是人类生命活动最普遍存在的一种节律形式,但这种节律周期可能被现代许多生活方式所破坏。人群流行病学和动物实验研究表明昼夜节律的紊乱与2型糖尿病的发病危险相关,但其机制尚未完全阐明。胰岛β细胞缺陷是2型糖尿病发生发展的必要机制,而昼夜节律紊乱与胰岛β细胞缺陷有一定关联。本文结合最新研究进展阐述昼夜节律紊乱与胰岛β细胞缺陷的相关性及其可能机制。     

Circadian rhythms of agitation in institutionalized patients with Alzheimer's disease

Agitation is a common problem in institutionalized patients with Alzheimer's disease (AD). “Sundowning,” or agitation that occurs primarily in the evening, is estimated to occur in 10—25% of nursing home patients. The current study examined circadian patterns of agitation in 85 patients with AD living in nursing homes in the San Diego, California, area. Agitation was assessed using behavioral ratings collected every 15 minutes over 3 days, and activity and light exposure data were collected continuously using Actillume recorders. A five-parameter extension of the traditional cosine function was used to describe the circadian rhythms. The mean acrophase for agitation was 14:38, although there was considerable variability in the agitation rhythms displayed by the patients. Agitation rhythms were more robust than activity rhythms. Surprisingly, only 2 patients (2.4%) were“sundowners.”In general, patients were exposed to very low levels of illumination, with higher illumination during the night being associated with less robust agitation rhythms with higher rhythm minima (i.e., some agitation present throughout the day and night). Seasonality was examined; however, there were no consistent seasonal patterns found. This is the largest study to date to examine agitation rhythms using behavioral observations over multiple 24h periods. The results suggest that, although sundowning is uncommon, agitation appears to have a strong circadian component in most patients that is related to light exposure, sleep, and medication use. Further research into the understanding of agitation rhythms is needed to examine the potential effects of interventions targeting sleep and circadian rhythms. (Chronobiology International, 17(3), 405-418, 2000)     

Disturbance of Circadian Rhythms in Analgosedated Intensive Care Unit Patients with and without Craniocerebral Injury

Melatonin, cortisol, heart rate, blood pressure, spontaneous motor activity, and body temperature follow stable circadian rhythms in healthy individuals. These circadian rhythms may be influenced or impaired by the loss of external zeitgebers during analgosedation, critical illness, continuous therapeutic intervention in the intensive care unit (ICU), and cerebral injury. This prospective, observational, clinical study examined 24 critically ill analgo‐sedated patients, 13 patients following surgery, trauma, or acute respiratory distress (ICU), and 11 patients with acute severe brain injury following trauma or cerebral hemorrhage (CCI). Blood samples for the determination of melatonin and cortisol were obtained from each patient at 2 h intervals for 24 h beginning at 18:00 h on day 1 and ending 16:00 h on day 2. Blood pressure, heart rate, body temperature, and spontaneous motor activity were monitored continuously. Level of sedation was assessed using the Ramsey Sedation Scale. The severity of illness was assessed using the APACHE‐II‐score. The time series data were analyzed by rhythm analysis with the Chronos‐Fit program, using partial Fourier series with up to six harmonics. The 24 h profiles of all parameters from both groups of patients were greatly disturbed/abolished compared to the well‐known rhythmic 24 h patterns in healthy controls. These rhythm disturbances were more pronounced in patients with brain injury. The results of this study provide evidence for a pronounced disturbance of the physiological temporal organization in ICU patients. The relative contribution of analgosedation and/or brain injury, however, is a point of future investigation.